1. Field of the Invention
The present invention relates to technology suitably used for a thin inner rotor motor for medium rotation driving used in, e.g., a floppy disk drive and the like.
2. Description of the Prior Art
Disk units such as floppy disk drives are in wide use with personal computers, office computers, and word processors, and are becoming remarkably widespread. This type of disk unit is constructed as shown in FIG. 10.
This type of disk unit is described briefly with reference to the drawing. In the drawing, the reference numeral 101 designates a chassis having a spindle center 102 as a disk rotation center thereof, which is housed in an equipment housing (not shown) of, e.g., personal computer, and is formed by a closed-end box that is open in forward and upward directions as a whole and has a housing space for housing a disk cartridge 103.
In a rearward portion of the chassis 101 are provided a stepping motor 124 for feeding a head carriage and the head carriage shuttled back and forth by the stepping motor 124. At the tip of the head carriage is held a first head 130 for reading recorded information from disk, and at a backward, upper portion of the head carriage is provided a head arm 132 having a second head 131 corresponding to the first head 130, the head arm 132 being swingably mounted through an elastic member. The head arm 132 is energized in a direction in which the second head 131 approaches the first head 130. The disk unit of this example is provided with a cartridge holder 136 for holding the disk cartridge 103 that can be freely inserted or removed, and a mechanism for opening and closing a shutter of the disk cartridge 103.
This type of disk unit is equipped with an inner rotor motor as shown in FIGS. 11A and 11B as a motor for rotating disk to meet recent demands for thinner disk units.
This comprises: an annular yoke 161 extending in a circumferential direction; a stator 164 having a large number of cores 163, provided radially in the inner circumference of the yoke 161, around each of which a coil 162 is wound; and a rotor 166 having an annular magnet 165 that is rotatably provided in the inner circumference of the stator 164 and faces the cores 163. The reference numeral 168 in the drawing designates a circuit board on which a holding part 170 incorporating a bearing 169 is mounted, and 171 designates a rotation axis for securing the rotor that is rotatably supported to the holding part 170 on the circuit board through the bearing 169 and extends vertically. The rotor 166 of the inner rotor motor functions as a turn table having a disk chucking magnet (not shown) and a disk chucking rotation lever (not shown).
In the inner rotor motor stator of this type, the yoke 161 and the cores 163 are provided to surround the almost entire circumference of the circular rotor 166 except the movement position of the heads 130 and 131. To satisfy the magnetic properties and other requirements, more expensive silicon steel plate than a galvanized steel plate is used to form the chassis 101 and other components.
However, for this type of disk unit, there have been a continued demand to reduce its manufacturing costs and a persistent demand to reduce the unit in size and weight.
For this reason, the inventor believes that there has been in an inner rotor motor stator a demand to reduce the space of the yoke 161 and the cores 163 that are made of expensive silicon iron.
However, if the space of the yoke 161 and the cores 163 is reduced to satisfy the above-described demand, magnetic interaction with the rotor 166 might become uneven in the circumferential direction and disk operation might become unstable.
Also, to reduce the space of the cores 163, the stator might be partitioned to have three cores. In this case, since the cores are often provided in parallel to each other, the interval between the tips of the cores would become too narrow, causing the problem that coils could not be wound.
The present invention has been made in view of the above circumstances and intends to achieve the following objects:
(a) reducing manufacturing costs;
(b) reducing the unit in size and weight;
(c) keeping motor rotation stable;
(d) increasing the operation stability of the disk unit; and
(e) pushing forward with reduction in stator size.
The above-described problems have been solved by an inner rotor motor of the present invention comprising: a rotor having plural magnetic poles disposed in a circumferential shape; and a stator including a stator core having plural magnetic pole teeth that are outside a circumference of the rotor and face the rotor, a coil being wound around each of the magnetic pole teeth, wherein the magnetic pole teeth are set so that the value of at least one of angles each formed by extensions of adjacent magnetic pole teeth is smaller than an angle formed by lines each connecting a tip center of one of adjacent magnetic pole teeth and a rotation center of the rotor.
In the present invention, the magnetic pole teeth may also be provided so that at least one of points of intersection of extensions of lines each connecting a base center and a tip center of one of adjacent magnetic pole teeth is in a position opposite to the magnetic pole teeth with respect to the rotation center of the rotor.
The magnetic pole teeth of the present invention can be placed so that extensions of lines each connecting a base center and a tip center thereof intersect at an identical point.
In the present invention, it is desirable that the magnetic pole teeth are provided so that intervals between the base centers of adjacent magnetic pole teeth are equal to each other.
Base centers of the magnetic pole teeth can be provided to be at an equal distance from a point opposite to the magnetic pole teeth with respect to the rotation center of the rotor.
In the present invention, it is desirable that the magnetic pole teeth are provided so that a value of at least one of angles each formed by extensions of adjacent magnetic pole teeth is 15 degrees or less.
It is desirable that the stator of the present invention is provided so that a central angle of the rotor with respect to the stator is in a range within 180 degrees.
Furthermore, it is desirable that six of the magnetic pole teeth are provided.
The disk unit of the present invention may include the above-described inner rotor motor.
In the present invention, the magnetic pole teeth are set so that the value of at least one of angles each formed by extensions of adjacent magnetic pole teeth is smaller than an angle formed by lines each connecting the tip center (tip center position) of one of adjacent magnetic pole teeth and the rotation center of the rotor. With this construction, in comparison with the case where magnetic pole teeth are provided radially from the rotor center as shown in FIG. 11, the interval between the adjacent magnetic pole teeth is reduced, and the space of yoke to which the magnetic pole teeth are connected is reduced, especially miniaturizing the stator and contributing to reduction in manufacturing costs.
The magnetic pole teeth are provided so that at least one of points of intersection of extensions of lines each connecting the base center and tip center of one of adjacent magnetic pole teeth is in a position opposite to the magnetic pole teeth with respect to the rotation center of the rotor. With this construction, it can be prevented that coils cannot be wound because of too small an interval between adjacent magnetic pole teeth.
Herein, the base center refers to the central position of a portion to which a magnetic pole tooth is connected to the yoke, in the circumferential direction of the rotor, and the tip center refers to the central position of a magnetic pole teeth face (rotor facing face) opposite to the rotor in the circumferential direction of the rotor.
The magnetic pole teeth of the present invention are placed so that extensions of lines each connecting the base center and tip center thereof intersect at an identical point. With this construction, the shape of the magnetic pole teeth can be set to be line-symmetrical with a line connecting the intersection point and the rotation center of the rotor. Thereby, in accordance with the magnetic pole teeth tip centers equally placed in the circumferential direction of the rotor, the stator can be made smaller and the interval between the magnetic pole teeth can be set so that coils can be wound.
In the present invention, the magnetic pole teeth are provided so that the intervals between the base centers of adjacent magnetic pole teeth are equal to each other. With this construction, the magnetic pole teeth can be made symmetrical with respect to a point of intersection of extensions of lines each connecting the base center and the tip center. Thereby, in accordance with the magnetic pole teeth tip centers equally placed in the circumferential direction of the rotor, the stator can be made smaller and the interval between the magnetic pole teeth can be set so that coils can be wound.
The base centers of the magnetic pole teeth are provided to be at an equal distance from a point opposite to the magnetic pole teeth with respect to the rotation center of the rotor. With this construction, the yoke to which the magnetic pole teeth are connected can be shaped to a simple arc, contributing to reduction in manufacturing costs.
In the present invention, the magnetic pole teeth are provided so that the value of at least one of angles each formed by extensions of adjacent magnetic pole teeth is 15 degrees or less. With this construction, the stator can be miniaturized, and especially the dimension of the yoke at each end thereof can be reduced, with the result that the amount of material such as silicon iron can be reduced, contributing to reduction in manufacturing costs.
The magnetic pole teeth of the present invention are provided so that angles formed by lines each connecting the tip center of one of adjacent magnetic pole teeth and the rotation center of the rotor are smaller than central angles at the rotation center of the rotor with respect to adjacent magnetic poles of the rotor. With this construction, the dimension of the stator core when viewed on a plan view can be reduced.
In the present invention, since the stator is disposed so that a central angle of the rotor with respect to the stator is in a range within 180 degrees, in comparison with the case where a stator is provided in the entire circumference of a rotor as in a conventional inner rotor motor, the space of a stator core can be reduced more than half. Therefore, the cost of stator core constructed from, e.g., silicon steel plate and the cost of coil windings can be reduced and the cost of manufacturing an inner rotor motor can be reduced. At the same time, in comparison with the case where a stator is provided in the entire circumference of a rotor, a space required to mounting a motor can be reduced to miniaturize the inner rotor motor, and the number of magnetic pole teeth can be reduced to reduce its weight. In addition to a stator placed within a continuous central angle of 180 degrees or less, plural stators may be placed discretely if the sum of corresponding central angles is within 180 degrees. If the stator is placed within a central angle of the rotor of 90 degrees or less, manufacturing costs, weight, and size can be further reduced.
In the present invention, six of the magnetic pole teeth can be provided to accommodate three-phase inner rotor motors.